Tag Archives: Geophysics

One of the more constraining factors of geophysical survey in an archaeological context is the potential difficulty in dating or phasing anomalies in the data. Although hard science forms the main component of survey work, there is a large subjective element involved in the interpretation of geophysical survey data, which ultimately can decide the nature, function and phase of features. Our interpretation sometimes belies the complexity of the archaeological remains in question (issues relating to survey resolution and the nature of deposits can affect this) and this is particularly true of the different phases of construction and occupation at a site. Complementary information on the phases of deposits represented in geophysical survey data can be provided through surface collection and recording over the survey area, and this integrated approach to archaeological survey is particularly pertinent to the recent Portuslimen survey conducted at Ephesus.

In August and September of 2015 a small team of archaeologists from the University of Southampton travelled to Ephesus in Turkey, to take part in the season of fieldwork run by the Österreichisches Archäologisches Institut (ÖAI). The ÖAI has conducted archaeological research at Ephesus for 120 years (http://www.oeai.at/index.php/grabungsgeschichte.html ), and for the last 16 years has conducted geophysical survey across the site, with work directed by Dr Sirri Seren of the Central Institute for Meteorology and Geodynamics (https://www.zamg.ac.at/cms/en/news). The Portuslimen team were invited to look at some very specific areas of the ancient site and landscape, namely the areas of the inner and outer Roman harbours, and the surrounding landscape of the river. The aim of the survey was to add to the areas already surveyed by the ÖAI, and to address the development and possible phasing of the harbour complexes of ancient Ephesus. The team comprised the author, together with Dominic Barker, Ben Urmston, Jack Pink and Jack Frowde.

Panoramic view of the area of the outer harbour and river as seen from the promontory

Magnetometry being undertaken at the inner harbour

To address these aims the team utilised fluxgate gradiometers, with gridding out and topographic survey conducted using an RTK GPS. Magnetometry was used in a field to the east of the inner harbour of Ephesus, and in fields around the outer harbour and river channel, also on the promontory overlooking the outer harbour.

In addition Electrical Resistivity Tomography (ERT) profiles were conducted at sites along the northern edge of the river channel, across the area of land between the outer harbour and river, and in the area of the floodplain to the north of the inner harbour. These were designed to assess the nature of the deeper sediments associated with the geoarchaeology of the landscape, for comparison with the borehole data collected by the University of Koln.

Although the geophysical survey techniques were deemed appropriate for the conditions of the site, the broad geographical range of the different survey areas,and the potential variations in phasing for the different results, presented the team with a problem; how to recognise the different periods of occupation in these areas, together with an idea of the character and function of many of the structures. To address these issues, fieldwalking was undertaken over each of the survey areas., utilising the grid set out for the geophysics, and using each of the survey markers as the central point for an area of surface material to be collected and recorded within a a 3m radius.

Set out of the survey grid using an RTK GPS

ERT survey to the north of the river channel

Surface collection to the north of the river channel, using the RTK GPS and note-taking

The method of sampling allowed collection of all pottery, with a record of presence and absence of CBM (? meaning )and building material. The collection of surface ceramics provides the diagnostic sherds necessary for establishing the type and chronology of the vessels, while its total collection over a small but standard sample area make it possible to calculate the count and weight of sherds and, thus, the potential ceramic density density in each area.

The results of the survey not only provided some excellent information about structures and port infrastructure in the different areas, but also provided some useful spot-dating of the potential phases of occupation of the areas. On the promontory overlooking the outer harbour a number of pit and gully features were found in the geophysical survey results, matching other surface evidence for Archaic settlement pre-dating the Roman harbour. The results of survey to the north and west of the outer harbour indicated large structures associated with the port, dating to the Roman and Late Antique periods. Finally the survey results to the north of the modern river channel detected structures and a possible canal that, when compared to the surface collection, seem to represent Late Roman and Byzantine phases of the port of Ephesus.

Location of surface collection points across the 2015 survey area

Roman amphora bases located to the west of the outer harbour

The results of the season are only preliminary, and further work needs to be undertaken on the data and at the site to fully understand the complexities of the changing harbours of Ephesus. However, a pattern is emerging which seems to indicate a gradual shift in the development of port infrastructure, with activity moving from the inner and outer harbours between the early Roman and Late Antique periods, to a later complex to the north of the modern river between the Late Antique and Byzantine periods. The evidence for pre-Roman occupation in the area is also of interest.

There are obvious caveats about the methodology that we have applied to the site, such as the depth of potential deposits and the nature of material exposed at the surface, which will ultimately affect the dating of material to particular periods of occupation. However, the combined strategy of surface collection and geophysical survey does provide us with a more nuanced data-set than with geophysics on their own, and has already started to raise interesting questions relating to the development and use of this fascinating port complex.

Over the past few months of field survey, work has swung around to a series of projects lined to Roman ports in the Mediterranean. In June and July I headed back for a season of excavations at Portus, and in August and September geophysical survey at the site of Ephesus in Turkey (more on this in a future post). In October and November work has commenced on a geophysical and topographic survey of the Roman port area of the town of Tarragona in Catalonia, Spain. The work, together with that of Ephesus, forms part of the Roman Meditteranean Ports (RoMP) project, or Portuslimen (http://portuslimen.eu/). A component of this project involves the survey of a number of port sites, to understand the form and extent of these sites, and help analyse the ways in which they may have functioned through time. The work at Tarragona is being conducted in collaboration with colleagues from l’Institut Català d’Arqueologia Clàssica (ICAC).

The modern port of Tarragona, with its harbour, docks and factories

The issue with Tarragona is that the development of the town and port spans from the pre-Roman period, to the establishment of the Roman town in the third century BC, to Late Roman and Visigothic settlement in the 6th, 7th and 8th centuries, and later Islamic influence. Over this time the town and its port expanded and contracted, and archaeological deposits were buried under fluvial deposits from the Francolí river to the west of the port. Later post-medieval expansion of the town, particularly in the 19th and 20th centuries saw much of the Roman and later port built over, and a new harbour constructed over the remains of the ancient port. The aim of our survey is to attempt to locate significant structural remins of the Roman port and harbour through intrusive methods. The good news is that a number of areas in the city have been excavated in the past 40 years, which helps in the location of the survey to gain as much as possible from the efforts. The bad news is that, due to the modern town plan, many of the survey areas are constrained by modern buildings and infrastructure. Thus our work has to use some specific techniques to conduct survey in the areas that are available. This includes topographic survey and location of survey grids using RTK GPS and total station survey, and use of GPR and ERT along streets and in plazas to map buried remains.

Set up of the GPS and GPR by the University of Southampton team in the Placa dels Carros

The GPS base station collecting static data for the survey

Fortunately for the University of Southampton team, the open plazas of the town provided sufficient space for static data to be collected by the GPS base station, and for a series of preliminary stations to be established using the GPS. Where the streets became narrow a total station was used to establish further stations in a traverse around the port area of the town.

Geophysical survey s far has focused on 500MHz GPR, propagating 3-4m below the modern street level to find the buried archaeology. In some of the streets in the northern part of the port area, particularly along the roads close to the Roman baths and theatre a number of walls and other features are visible. As the survey progresses southwards, however, modern infrasructure such as manhole covers, and the nature of the made-up ground close to the modern harbour, make the results more difficult to interpret. The restrictions in terms of spatial coverage have also provided a challenge in terms of data interpretation.

Total station survey in one of the streets of Tarragona

500MHz GPR survey in one of the plazas

To better understand the geoarchaeology of the site we have been applying Electrical Resistivity Tomography (ERT) to record both archaeology and deeper deposits in the town. The main constraint with this is that the paved areas of the town preclude the use of survey probes (these cannot be dug through cement and Tarmac). Thus we have had to adapt using a system of electrode copper conductors and a conductive gel. Most surfaces will allow an electrical current to be passed through them, but asphalt and Tarmac act as insulators, meaning that for the ERT to work long stretches of cement pavement need to be surveyed.

A conductor formed from crocodile clips, wire and pipe end copper usually used for plumbing.

The ERT profile being conducted adjacent to the Roman theatre

In spite of our initial misgivings, the conductors and gel, with the ERT equipment, have proved to work very well indeed. The profile alongside the Roman theatre has revealed a number of areas of walls and rubble aligned adjacent to the excavated theatre remains. The team hope to conduct a long profile of ERT in the southern part of the modern port which, together with the boreholes of Ferreol Salomon, will investigate the nature of the harbour deposits.

The survey work is being conducted until 15th November, and there are many features of the topography of the ancient harbour that remain to be discovered, including the line of the Roman seafront and mole.

Back in 2011 the Theban Harbours and Waterscapes Survey (THaWS) started with a field season of geophysics. This Egypt Exploration Society project (www.ees.ac.uk), directed by Dr Angus Graham, was established with the aim of using different techniques to study the settlements and temples on the east and west banks of the Nile, and how they relate to the changing floodplain and river. Unfortunately the season had to be aborted after the 25th January revolution, and the survey was postponed to the 2012 season, when the fieldwork progressed at a cracking pace.

After five years of the project a large quantity of survey data, together with sedimentary data from auger samples, has been collected and is pushing forward some tentative interpretations about the archaeology and geomorphology of the area. Fieldwork in areas as diverse as Malqata, Birket Habu and the floodplain in front of Kom El Hetan and the Ramesseum has provided food for thought on the depth of ancient ground levels and the organisation of the waterways on the West Bank, with interesting results from some of the East Bank work, including Karnak.

For the 2015 season the fieldwork has shifted up a notch with a larger and more diverse team. The plan was to run different geophysical survey techniques, while also continuing the auger sample strategy and processing of samples from the 2014 and 2015 seasons. Work has very much focused on Electrical Resistivity Tomography (ERT) surveys on the West Bank, particularly in the area to the east of the Ramesseum heading up to the current course of the Nile, with Ginger Emery working on the instrument. This has been complemented by an intensive season of auger work conducted by Ben Pennington and Willem Toonen, to investigate changes in the sediments represented in the ERT.

ERT survey under way on the West Bank

Auger work along ERT profile 32, West Bank

The survey has allowed a solid dataset to be collected running from c.600m to the east of the Ramesseum all the way the the modern banks of the Nile, with the resistivity and auger data integrating to allow some more nuanced interpretations of the development of the floodplain and the presence of possible man-made canals to be ascertained. The work in this area relates closely to the function of temples further to the south between the Birket Habu and the Ramesseum.

ERT profile running at the foot of the Colossi of Memnon, Kom El Hetan

This week we have focused the work in the area of Kom El Hetan. Previous seasons provided information on the axis of theTemple of Amenhotep and the possible presence of channels associated with the temple. The aim this week has been to expand on this information with more intensive ERT and Ground Penetrating Radar (GPR) survey in the area.

ERT survey at Kom El Hetan

Hopefully by the end of the week we will have a series of close (5m) profiles of ERT data to model, and GPR data at 0.5m intervals across the front of the Colossi, in the first court, and in the third court for comparison, with a second plan to conduct more GPR profiles in the fields to the south to detect the possible enclosure of the temple. It promises to be an exciting week.

There have been trials and tribulations in the fieldwork, including negotiations with landowners, and issues with the burning of sugar cane chaff during the first two weeks. There have also been compensations, not least in the form of tea and cake, the latter being provided by the wife of Sumara, one of our workmen.

Burning sugar cane chaff promises to engulf the ERT equipment

Husam cuts the cake provided by Sumara’s wife. One of the perks of fieldwork in Egypt!

The fieldwork will be carrying on at Thebes until 1st April. However, results from the previous seasons of work are presented in the last three editions of the Journal of Egyptian Archaeology, and in other papers listed below. Happy reading!

For the last few weeks a fair amount of preparation has been undertaken by various members of staff at the University of Southampton for a press release on the fieldwork conducted at Old Sarum (see previous blog post https://kdstrutt.wordpress.com/2014/04/21/in-the-castle-called-seresberi-old-sarum-and-a-new-survey-of-the-inner-and-outer-baileys/). Peter Franklin and colleagues at the press office have worked hard to produce the finished story, and today things finally came together with a bit of a whirlwind of media attention. The finds of the project to date illustrate the potential of non-intrusive archaeological methodologies to elucidate on the archaeology of a particular site or landscape, without harming the material culture and with some strong underlying scientific concepts on which to base some degree of interpretation and narrative.

The step from geophysical survey data to coherent archaeological narrative is a big one, and one of the reasons that our interpretations to date err on the side of caution. What is apparent from the results is the urban plan of a substantial medieval city, and an array of different forms of structure and associated features in the outer bailey at Old Sarum. Hopefully the results and their wider dissemination at this stage will help to generate interest in the site, the methodology used, and the wider applications of these approaches to archaeological research.

To date the results have been reported in a number of sources. Online the sources include:

More will hopefully follow tomorrow. Above all else the results show the pertinence of student involvement in research-led teaching, from developing an understanding of the archaeological and scientific theory for the work, to dealing with practical aspects of survey and undertaking fieldwork, to being involved in the processing and interpretation of data. The results at Old Sarum are testament to the peerless hard work and dedication of the students on the project, as well as the staff involved in their supervision.

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Due to commitments in the field over the last month or so it has proved difficult to keep up to date with the blog. Now seemed like a good time to produce a few posts to highlight some recent fieldwork and site visits, starting with a recent survey at Naukratis. In May 2014 I conducted geophysical survey at this archaeological site in the Nile Delta. The Naukratis fieldwork project is directed by Ross Thomas of the British Museum, and seeks to assess the surviving archaeology of this important ancient site using a range of complementary methods including topographic and geophysical survey, in addition to borehole survey and excavation, as part of a larger project directed by Alexandra Villing of the Greek and Roman department of the British Museum called ‘Naukratis: Greeks in Egypt’.

Magnetometer survey being conducted to the east of Kom Ge’if

The season in May (the third season of fieldwork) added to the existing dataset from the first two seasons in 2013, mapping the extent of the ancient settlement and its association with the Canopic Branch of the River Nile.

The port of Naukratis was the earliest Greek port in Egypt, established in the late 7th century BC as a base for Greek (and Cypriot) traders and the port of the royal Pharaonic city of Sais. It was an important hub for trade and cross-cultural exchange long before the foundation of Alexandria and continued to be significant through the subsequent Ptolemaic, Roman and Byzantine periods. Previous fieldwork was conducted by Flinders Petrie amongst others, and concentrated on excavation of the central areas of the ancient town. Further research was required to fully understand this very important archaeological site. For this season, the magnetometer survey of the site was continued in the fields surrounding the modern village.

Two ERT profiles were also undertaken using an Allied Associates Tigre ERT. The first of the profiles ran from a point some 400m to the west of the site, over the kom or mound, to a point 400m to the east of the site, incorporating the line of the Canopic Branch of the Nile and Naukratis. This provided a section 15m deep running west-east across the southern part of the site. The main aim was to better understand the geological relationship between the river and the settlement, and to tie the profile in with the series of borehole surveys conducted along the same traverse.

Mohamed Roshti assisting with the ERT survey on the kom

The survey work at Naukratis has produced significant new data on the layout of the ancient town, its local environment and hinterland, including the location of the Greek sanctuary complex, the Hellenion, and the Temenos or temple enclosure at the site. The magnetometer results located a large number of mud brick and stone structures in the fields around Kom Ge’if, particularly in the north and east of the site. In addition to the plan of the ancient town, the magnetometer results also give us a much better idea of the extent of the ancient site in relation to the location and development of the Canopic branch of the Nile, which ran to the west of the ancient settlement. The magnetometry clearly shows the change from settlement to canal infilling, with structures positioned along the edge of the canal. This data is reinforced by the results of the ERT survey. The depth of deposits underlying and surrounding Kom Ge’if is suggested by the topography, with a sharp contrast between the kom and the surrounding fields. The remains of the ancient site are present, if buried, but life in the modern village of Kom Ge’if carries on. The village, with its new mosque, stands out from the surrounding floodplain, a mixture of bean fields, and brown ploughed and saturated fields prepared for planting melon. A number of venerable sheikhs’ tombs stand out on the fringes of the village. The local shepherd crosses from field to field, allowing his sheep and goats to graze on the stubble remaining from the wheat harvest, and manuring the fields in the process, then herds the flock back through the winding streets of Kom Ge’if.

Detail of survey results from Naukratis

Many of the areas of the ancient settlement still require surveying using magnetometry, and a combined strategy of ERT survey with drilling of boreholes will provide useful comparative data for particular parts of the site and its hinterland.

The current season of THaWS fieldwork has given the team some time for reflection on the survey results from 2012 and 2013, and has provided an opportunity for addressing some of the outstanding issues related to the mapping of Thebes on the west and east banks. Survey work throughout the 2012-2014 has been carried out by the team members, including the project director Angus Graham, who oversees the work with the Egypt Exploration Society (EES; http://www.ees.ac.uk/), Sarah Jones from the Museum of London (MOLA) and Dominic Barker and the author from the Department of Archaeology at the University of Southampton. In 2012, due to some problems with equipment, much of the surveying in of the geophysical survey areas and profiles was conducted using a total station. In 2013 an RTK GPS was used for surveying topographic points and giving elevation data for the topographic correction of GPR and ERT profiles. While these surveys gave sufficient data for processing and interpreting the results of the geophysics, it still left some largely unanswered questions in the minds of the team. How does the current GPS survey relate to the existing local surveys on the west and east banks at Thebes? What remaining survey markers or stations exist in the landscape, allowing THaWS to tie material in to the current survey? Most importantly perhaps, we returned to the issue of what elevation above sea level to use for the project. THaWS is interested in looking at the increasing levels of Nile sediment over thousands of years, and how the natural and man-made changes to the floodplain relate to the archaeology of the area. Having a standard benchmark or datum for this is crucial.

Assessing the different surveys and coordinate systems utilised around Thebes, using sketches and charts, the Survey of Egypt and Reimer maps and field notes

The first step in relating the different local surveys in the study area was to list and assess the nature of the different coordinate systems and datums utilised by different surveys.

It is good to give a bit of historical background to the mapping in the area. The data that we have relate ostensibly to national mapping programmes, or individual projects utilising local or arbitrary coordinate systems. We also have mapping dating from the 19th century, in the form of sketch maps and plans. Of these the map data that has provided the most relevant data is the map produced by John Gardner Wilkinson (1797-1875). Wilkinson published The Topography of Thebes and General View of Egypt in 1835, describing the monuments and landscape around Thebes. No graticule is present on the map, and no information regarding datum or coordinate system are presented. The map does, however, relate standing archaeological remains with features on the Nile floodplain, and therefore provides a crucial document in building up a picture of the study area.

A detail of Wilkinson’s map

The maps that are perhaps most pertinent to the THaWS work are those produced by the Survey Department between 1892 and 1907 for the cadastral mapping of Egypt. Lyon’s 1908 description of the cadastral survey includes some notes on technical aspects of the survey, including the use of metal chains and some of the practicalities of surveying this vast country. The maps based on the Survey of Egypt for Thebes all utilise the Egyptian Red Belt datum and the Survey of Egypt coordinate system. These systems were also adopted by the map produced by Schweinfurth, published by Reimer in Berlin in 1909, and drawing on Wilkinson’s map, the Survey of Egypt cadastral survey.

One of the principal aims of the 2014 survey was to try and locate trig points and bench marks created by the Survey Department for the cadastral mapping of Egypt. Locating the remaining markers is, however, another matter. The reconnaissance in 2013 and this season has found only two markers; one a trig point above El Gorn on the heights above the Valley of the Kings, and a benchmark on the corner of the wall of one of the alabaster shops to the south of Hatshepsut. The lesson from this experience is clear: the survival of even official survey markers in the landscape at Thebes is unlikely.

Survey marker on the heights of Biban el Muluk, one of the only markers in the area of El Gorn where the marker survives

Survey benchmark at the alabaster shops to the south of Hatshepsut

In addition to the national and regional mapping projects being assessed, many of the local surveys on the east and west banks are of relevance to the project. In particular survey of markers from the Theban Mapping Project (http://www.thebanmappingproject.com/) and markers from the ongoing project work at the temple of Amenhotep III provide useful ancilliary data for the THaWS work. These surveys use their own local coordinate systems, however, the use of reduced heights above sea level for the projects makes the survey of points vital to allow current survey data to be related to existing publications showing the relationship between monuments and the ancient Nile flood levels.

Survey this season with the GPS allowed a transformation to be performed between the UTM 36N coordinate system with WGS84 datum being used by the GPS, and the Theban Mapping Project survey markers. The result of this shows some large error caused by the probably moving of survey markers within the landscape over the last 20-30 years. The systems of these projects give useful elevation information that is germain to the aims of the current THaWS work.

Dominic Barker and Kamal Helmy Shared positioning the GPS rover on a survey marker at the temple of Merenptah

One final set of survey data has been essential for resolving the issues surrounding elevation: the survey datum and account of Hölscher for the excavations at Medinet Habu. A datum point, set at 0m, was established by Hölscher on the threshold of the first pylon at Medinet Habu. He wrote:
‘For the leveling of Medinet Habu the threshold of the first pylon was chosen as the zero-point. This point lies 77.09 meters above sea-level. A bench mark of the Survey Department on top of the granite threshold between the two guardhouses of the Eastern Fortified Gate stands at +76.82 meters, that is, 27 centimeters lower than our zero-point of leveling.’

(Hölscher 1934, 3)

Although the Survey Department benchmark is no longer visible, the stones on either side of the central axis at the threshold remain in situ, and provided a useful datum to record with the GPS. In fact when this point is considered together with the other points of elevation on the West Bank there is a discrepancy of 0.12m over points spread some 5km across the landscape, a considerable achievement in terms of the accuracy of the original Survey Department benchmarks and the traversing of these elevations to the different projects concerned. For the THaWS survey we are now in a much better position to use a suitable benchmark for elevation above sea level that relates to the work and published material of the different projects at Thebes.

Kamal Helmy Shared and Dominic Barker surveying on top of the mounds at Birket Habu

There is still work to do in relating our survey data with work on the West Bank and at Karnak to ensure that THaWS data is compatible with other datasets, in terms of spatial location and elevation. However, the relationship between our geophysical survey and borehole data, our current survey, and its relationship to other survey data at Thebes, is perhaps more transparent and congruent to existing material.

References
Hölscher, U. 1934, The Excavation at Medinet Habu. Volume 1 General Plans and Views. The University of Chicago Oriental Institute Publications Volume XXI. Chicago; University of Chicago Press.
Lyons, H.G. 1908, The Cadastral Survey of Egypt 1892-1907. Cairo; National Printing Department.
Wilkinson, J.G. 1835, Topography of Thebes and General View of Egypt, being a Short Account of the Principal Objects Worthy of Notice in the Valley of the Nile. London; John Murray.

The second week of survey at Basing House finished on Friday in a spray of mud and rain, hailstones and inky cloud. What had promised to be a reasonable day quickly became unworkable, wet and cold. The teams set out for the final day of survey, focusing on completion of the magnetometry and resistivity in the area of the New House and outer bailey, and GPR over the outer bailey also. We abandoned the magnetic susceptibility to ensure that all hands were working on the res and mag. The rain set in and the GPR survey was the first to suffer, with the notebooks turning to mush.

Time for a weatherproof notebook!

The magnetometry continued, mopping up grids on the Civil War earthworks, and finishing the survey of the New House and outer bailey. Resistivity was completed in the Old House and the New House, although the team had suspicions that the wet weather would affect the results.